JP2024513908A - optical detector - Google Patents

Abstract

The present invention relates to an optical detector (100) with improved sensitivity for detecting optical signals originating from larger angles of incidence. The optical detector (100) may also be used to determine the direction of departure of an optical signal. The optical detector (100) includes a photodetector (101) and a lens (103). The photodetector (101) has a central axis (102) located in a central plane (001) perpendicular to the photodetector plane (002). The lens has a first lens segment (131) and a second lens segment (132) separated by the central plane (001). The first lens segment (131) includes a first light receiving surface (133) and a first light exit surface (135), the first light exit surface (135) facing the photodetector (101). The second lens segment (132) includes a second light receiving surface (134) and a second light exit surface (136), the second light exit surface (136) facing the photodetector (101). The first light receiving surface (133) includes a first convex surface having a non-constant curvature, the first convex surface having a first minimum radius of curvature (051) at a first surface point. The second light receiving surface (134) includes a second convex surface having a non-constant curvature, the second convex surface having a second minimum radius of curvature (052) at a second surface point. A first angle (053) enclosed by the central axis (102) and a first line (055) is greater than 0 degrees, the first line (055) is perpendicular to the first convex surface at the first surface point and extends to the central axis (102). A second angle (054) subtended by the central axis (102) and a second line (056) is greater than 0 degrees, and the second line (056) is perpendicular to the second convex surface at a second surface point and extends to the central axis (102).

Description

The present invention relates to an optical detector configured to better receive optical signals originating from a wide viewing angle. Additionally, the optical detector is configured to robustly determine the direction of incoming optical signals from multiple directions. Optical detectors may be suitable for, but are not limited to, optical wireless communication.

In recent years, optical wireless communications has experienced rapid growth in research and commercial activity. High speed, high bandwidth, immunity to electromagnetic interference, and security are attractive features driving these activities. Briefly, this is the field of communications where modulated visible, infrared, or ultraviolet light is used to transmit communication signals in the form of optical signals. This component is configured to transmit optical signals in a wide beam and is often referred to as an access point, which is connected to an information network. In a common scenario, multiple access points are installed on the ceiling to cover as much of the target area as possible. Each access point, including an emitter, may be incorporated into a ceiling light fixture. The receiving side includes an optical device including at least a photodetector arranged to receive these transmitted optical signals and establish a communication link with at least one of the access points. be. The receiving side may also include an emitter configured to emit a wide beam of optical signals that is received by one or more photodetectors at the ceiling access point. The receiving side is often called an endpoint. Both access points and endpoints are essentially optical wireless communication devices that contain at least components such as emitters, photodetectors, and necessary communication circuitry.

Endpoints of optical wireless communication systems may detect optical signals using photodetectors in combination with imaging optics. Generally, the amount of light reaching the detector decreases with the cosine of the angle of incidence relative to the detector surface (as the projected area decreases). Furthermore, for optical wireless communications where the receiver is translated in a plane parallel to the plane in which the emitter is located, the distance increases (again with the cosine of the angle) for larger angles of incidence. Additionally, an emitter may emit lower intensity at larger angles to its emission axis (eg, in the case of Lambertian emitters, again with the cosine of the angle). That is, the cosine has three dependencies that result in a strong drop in the detection signal as the angle of incidence increases. As the angle of incidence increases (i.e., as the translation of the endpoint with respect to the access point position increases), the detected signal as well as the detected power becomes much smaller, dramatically reducing the communication link speed or link It can even cause losses. Conversely, emitters can transmit optical signals at high intensities and the required power losses are too large to be incorporated into small building blocks (e.g., mobile phones) as required in consumer applications. I can't.

A photodetector may include multiple detector segments for determining the direction of an incoming optical signal. Even with the use of imaging optics with multiple photodetector segments, the access point emitter is so small that it does not provide accurate directional information and, as a result, provides little direction information for many different directions of the incoming optical signal. yielding the same detector signal. Although it is possible to know in which photodetector segment an optical signal was received, it is not possible to know exactly where the optical signal originates. Also, for the reasons mentioned above, it becomes difficult to achieve sufficient angular discrimination when the optical signal originates from a wide viewing angle.

It is therefore desirable to increase the gain of the optical element at larger angles of incidence or viewing angles to substantially improve the sensitivity of the photodetector.

It is an object of the invention to provide an optical detector with improved sensitivity for larger angles of incidence. Therefore, the optical detector is better able to detect optical signals incident from larger angles of incidence. The optical detector is also configured to robustly determine the approximate direction of the incoming optical signal. Additionally, the optical detector is an optical wireless communication device that detects the optical signal and determines the orientation of the access point or endpoint relative to the optical detector, further assisting in transmitting the narrow beam optical signal in a particular direction. device).

According to a first aspect, this and other objects are achieved by an optical detector for receiving incoming optical signals from multiple directions. The optical detector includes a photodetector and a lens. The photodetector has a central axis located in a center plane perpendicular to the photodetector plane. The lens has a first lens segment and a second lens segment separated by a central plane. The first lens segment includes a first light receiving surface and a first light exit surface, the first light exit surface facing the photodetector. The second lens segment includes a second light receiving surface and a second light exit surface, the second light exit surface facing the photodetector. The first receiving surface includes a first convex surface having a non-constant curvature, the first convex surface having a first minimum radius of curvature at a first surface point. The second light-receiving surface includes a second convex surface having a non-constant curvature, the second convex surface having a second minimum radius of curvature at the second surface point. a first angle subtended by the central axis and a first line is greater than 0 degrees, the first line being perpendicular to the first convex surface at the first surface point and extending to the central axis; . A second angle subtended by the central axis and the second line is greater than 0 degrees, the second line being perpendicular to the second convex surface at the second surface point and extending to the central axis.

The convex surface allows concentration of the impinging optical signal as long as the transmission medium has a higher refractive index. Therefore, by orienting the convex surface obliquely to the normal direction (the normal direction coincides with the central axis of the lens), it is possible to increase the concentration of light from a certain oblique direction. can.

A convex surface may have one or more radii of curvature. For such a curve, the radius of curvature at a point is equal to the radius of the arc that best approximates the curve at that point. The minimum radius of curvature may refer to a global or local minimum radius of curvature. The first or second angle indicates the orientation of this point of highest curvature of the convex surface. A light signal impinging around a first surface point or a second surface point of the convex surface, whose impingement direction coincides with the first line or the second line, is compared to other parts of the convex surface having a lower curvature. and experience greater concentration. Therefore, the optical detector can have improved sensitivity to optical signals having a direction that is aligned to some extent with the first line or the second line.

The lens may have a lens field of view. The first and second lens segments may have segmented fields of view. The segmented field may be a subset of the lens field. The segmented fields of view may be substantially different, but may have viewing areas that overlap about a central axis. One way to vary the degree of overlap between fields of view may be by modifying the light receiving surface of the lens segment.

The first angle and the second angle may have the same value in the range of 5 degrees to 45 degrees.

The first lens segment and the second lens segment may be mirror symmetrical or rotationally symmetrical about the central axis.

The possible choices of convexities and their orientation are quite wide. The choice is the full field of view (FoV) required by the application, and how low the concentration can be tolerated for other angles of incidence (an increase for one angle of incidence means a decrease at other angles of incidence). may depend on.

For optical wireless communications, it may be preferable for the first angle and the second angle to be on the order of 5 degrees to 45 degrees.

The first light receiving surface and the second light receiving surface have portions adjacent to the central plane, which may be substantially flat or concave.

An optical signal originating from a direction that coincides with the central axis may mean that the optical signal is likely to originate from the shortest distance. Therefore, the strength of the optical signal will be much stronger compared to optical signals originating from other locations. Therefore, by choosing a concave or flat surface, a sacrifice may be made to reduce the gain or concentration for optical signals originating from directions coincident with the central axis.

The first light-receiving surface and the second light-receiving surface may have a portion adjacent to the central plane that curves toward the photodetector plane.

The first light receiving surface and the second light receiving surface have portions adjacent to the central plane that may be configured such that tangents to the portions of the first light receiving surface and the second light receiving surface can be extended to intersect the central plane and the photodetector plane.

This configuration may result in stronger reductions in gain or collection for optical signals originating from directions coincident with the central axis. Therefore, this configuration may be selected if such conditions are non-trivial. However, such a stronger reduction for on-axis (center axis) detection may allow a stronger increase in gain or concentration for off-axis detection (away from the center axis).

The lens may have a lens edge surface around the edge of the photodetector. The lens edge surface may have a partial coating. The lens edge surface may be orthogonal to the photodetector plane. The partial coating has an outer portion that may be absorptive or reflective and an inner portion that may be reflective. The reflective nature of the inner portion allows folding of incoming light from high incidence angles that cannot be focused by the lens to the photodetector plane. The partial coating may be achieved by a metal sheet or a reflective coating configured on the lens edge surface.

Alternatively, the lens edge surface may be free of any form of coating.

Furthermore, the lens edge surface does not have to be orthogonal to the photodetector plane.

The photodetector may include a first photodetector segment and a second photodetector segment configured about a central axis.

The above lens may be combined with a segmented photodetector to enable the direction detection capability of the optical detector.

The photodetector can be a PN or PiN photodiode (PD), an avalanche photodiode (APD), a phototransistor, a silicon photomultiplier (SiPM) or a multi-pixel photon counter (MPPC), a single photon avalanche detector (SPAD), etc. However, SiPM/MPPC and SPAD as well as other detectors may include multiple segments. The photodetector segments may be arranged concentrically or hexagonally packed. The photodetector segments may also be arranged in a straight line.

The first light exit surface may be in optical contact with the first photodetector segment and the second light exit surface may be in optical contact with the second photodetector segment.

In this case, "in optical contact" may be interpreted as allowing optical transmission between two parts that are in optical contact.

If the lens and photodetector are separated by air, air may be considered a coupling medium. However, more Fresnel reflections at the interface of the lens facing the photodetector can result in greater light loss. Therefore, a medium with a higher refractive index than air is preferred. Otherwise, the photodetector and lens may have an anti-reflection coating to prevent or at least minimize light loss.

The optical contact can be a thin optical bonding layer, weak van der Waals interaction adhesion, or a direct interconnect realized, for example, by molding or casting. can. If the photodetector is in contact with the lens by means of a coupling material, it may be advantageous to have the coupling material with a refractive index between the refractive index of the lens and the photodetector, preferably the refractive index of the lens and/or the coupling material. is chosen relatively close to the refractive index of the photodetector.

The first and second lens segments may be at least partially optically isolated from each other by an optical isolator about the central axis.

"At least partially optically isolated" means that the first and second lens segments are two separate segments and that no light impinges on the separation between the segments. may be interpreted as leading to full reflection or partial transmission. This degree between full reflection and partial transmission may be subjective to the angle of incidence.

The optical isolator may be an air gap between the first lens segment and the second lens segment.

The air gaps may be arranged symmetrically about a central plane. At relatively high angles of incidence, the incoming optical signal may not be completely focused on the associated photodetector segment and therefore may reach the air gap. The air gap may be designed to allow at least partial transmission of optical signals on neighboring photodetector segments and promote crosstalk. Additionally, the air gap is designed to reflect a substantial optical signal to the photodetector segment(s) associated with the receiving lens segment, thereby increasing the signal strength per unit sensor area used for this detection. It's okay. Although this crosstalk behavior is extremely undesirable for communications, it can be exploited for robust determination of the originating direction of an incoming optical signal. Also, if the lens segments are completely optically isolated from each other by reflective material, determination of the direction of origin of the incoming optical signal may be possible, albeit with less precision.

If it is desired that the optical detector be used to detect and demodulate optical signals, the optical isolator or air gap may be designed to have limited optical transmission leading to limited crosstalk. . For example, depending on the angle of incidence, light transmission through an optical isolator or air gap may be no more than 10% of the light impinging on the optical isolator or air gap. More preferably, 5% of the light striking the optical isolator or air gap may be allowed to be transmitted.

The air gap has a width that may range from 10 to 100 micrometers.

The first lens segment and the second lens segment are positioned about a central axis and have substantially opposing edge surfaces, the edge surfaces being at least partially transmissive material. ) may be included.

The air gap and the at least partially transparent material may together represent an optical isolator. The at least partially transparent material in the form of a coating or film may be a thin metal or dielectric film (e.g. _SiO2 , SiNx, _TiO2 , and Al) having reflective properties but preferably no scattering properties. ₂ O ₃ ) or a combination thereof.

The first and second lens segments may be manufactured separately, with adjacent edge surfaces at least partially covered with a transparent material, and assembled to have the above-described configuration of the lens.

The optical isolator may be a partially transparent material located between the first and second lens segments.

The at least partially transparent material may be selected to be fully reflective or partially transparent.

The lens may have a number of lens segments, and the photodetector may have a number of photodetector segments equal to or an integer multiple of the number of lens segments.

A higher number of photodetector segments per lens segment may be beneficial for accurate determination of the direction of the incoming optical signal.

According to a second aspect of the invention, an optical wireless communication device is provided. The optical wireless communication device includes the optical detector and signal processor described above. The signal processor is configured to receive a plurality of detector signals generated by the first photodetector segment and the second photodetector segment. The optical wireless communication device further includes a demodulation device. The signal processor is configured to select at least one of the plurality of detector signals, and the demodulation device is configured to demodulate at least one of the plurality of detector signals to extract data. .

The signal processor may be a microprocessor, microcontroller, or one or more comparators.

The detector signal can be the quantified power or amplitude of the detection signal measured by the photodetector segment.

For communication purposes, high frequency modulation is used. The modulation may generally be in the form of amplitude modulation, such as on-off keying (OOK), non-return-to-zero on-off keying (NRZ-OOK), or in the form of X-level pulse amplitude modulation (PAM-X), such as PAM-3 or PAM-4. Alternatively, a form of frequency modulation may be used, or further combinations of modulation techniques may be used, such as optical orthogonal frequency division multiplexing (OOFDM). Common to all modulation techniques used here is the modulation of the light beam, typically at a relatively high frequency, for example 1 MHz or higher, to transmit the actual data. Therefore, a high pass filter may be used to filter the detector signal before it is received by the signal processor. The high pass filter may pass signals at 1 MHz or higher. To extract the data or information from the detector signal, demodulation is required.

A signal processor may determine which signals may be used for demodulating and extracting data or information from the detector signal. Therefore, the signal processor may select either or both detector signals for demodulation by the demodulation device. Optical wireless communication devices may support multiple input single output (MISO) systems.

The optical wireless communication device may further include an optical signal emitter and a controller. The optical signal emitter may be configured to emit a transmitted optical signal in an emission direction that is tunable, and the controller may be configured to control the optical signal emitter. The signal processor may be configured to determine the direction of the incoming optical signal by comparing the plurality of detector signals, and the signal processor may be configured to adjust the emission direction of the optical signal emitter based on the direction of the incoming optical signal. The controller may be communicatively connected to the controller.

Optical detectors serve the following functions in optical wireless communication devices: 1) detect optical signals with enhanced off-axis gain; and 2) determine the direction of an incoming optical signal.
It may be used in two roles.

Alternatively, the optical wireless communications device may include an optical signal emitter that may be configured to emit a transmitted optical signal with an emission direction that is adjustable, a controller configured to control the optical signal emitter, and a direction sensor including an optical element and a segmented detector. The signal processor may be configured to determine the direction of the incoming optical signal by comparing a plurality of sensor signals generated by the segmented photodetector. The signal processor may be communicatively connected to the controller to adjust the emission direction of the optical signal emitter based on the direction of the incoming optical signal.

In this case, the optical detector has the single role of detecting the optical signal with enhanced off-axis gain. On the other hand, the direction of the incoming optical signal is determined by a direction sensor. The direction sensor may be an inexpensive optical sensor that includes an optical element and a segmented photodetector. Optical elements can be imaging or non-imaging.

A low pass filter may be used to filter the detector signal to determine the direction of the incident beam or light. If the optical wireless communication signal is modulated to, for example, 100 MHz, direction detection may be performed with the signal low-pass filtered at 1 MHz, or even 100 kHz. Alternatively, a 1 kHz to 100 kHz bandpass filter may be used for direction detection, as near direct current (DC) signals may also need to be filtered out.

A detector signal filtered by the low-pass filtered signal may be received by a signal processor, and the signal processor may be configured to determine a fraction of the detector signal. An example of a fraction can be the magnitude of the detector signal detected by a photodetector segment divided by the sum of the magnitudes of the detector signals from all photodetector segments. By comparing the fractions of the detector signals, the direction of the incoming optical signal can be determined.

The maximum fraction of the low frequency response of the detector signal may be used to determine from which photodetector segment the communication signal should be extracted, thus providing a single Only one trans-impedance amplifier (TIA) may be used.

Alternatively, high-pass filtered optical communication signals from different photodetector segments can be used to determine the direction of the incident beam, but this requires multiple transimpedance amplifiers with high frequency amplification characteristics. shall be.

To determine only the relative orientation of the access point(s) or endpoint(s), the bandwidth of the photodetector is less than 10% of the bandwidth of the incoming optical signal to enable even higher sensitivity. can be. Preferably, the 3 dB frequency bandwidth of the photodetector in the direction sensor can be less than 10% of that of the photodetector in the signal sensor used to detect incoming optical signals at high modulation frequencies. It may be even lower, such as <1% or even <0.1%.

Suitable examples of optical signal emitters include LEDs, superluminescent light-emitting diodes (SLEDs), edge-emitting laser diodes (ELDs), and vertical cavity surface emitting lasers (VCSELs). vertical-cavity surface-emitting lasers) and can have either a single emitter or multiple emitters (or emitting segments).

The optical signal emitter may be configured to emit an optical signal in an emission direction that is adjustable within the emitter field of view. The beam of transmitted optical signals may preferably have a narrow beam. The use of directional and narrow emission of radiation to the targeted receiver location may allow the intensity within the beam shape to be increased considerably. Therefore, a reduction in energy dissipation can be expected with an increase in data rate. Furthermore, a smaller volume can be used because there is less heat dissipation, and eye safety can also be improved because the total optical power that needs to be emitted is lower.

The optical signal emitter may be configured to emit at a solid angle subtended by less than 60%, preferably less than 30%, and most preferably less than 15% of the lens field of view.

The controller may be configured to control the optical signal emitter. Control of the optical signal emitter may include adjustment of the emission direction and control of basic emitter characteristics (eg, intensity, modulation frequency, and wavelength adjustment).

The controller may also be responsible for receiving downlink or uplink signals from the network or endpoint devices, respectively, and converting them to be compatible with optical wireless communications.

It should be understood that the optical detectors of all configurations described herein above may be suitable for use in an endpoint or access point device from an optical wireless communications system. The purpose of the optical detector may be solely to detect the optical signal and/or to determine the source or access point location.

Once the direction of the access point is determined by the signal processor from the incoming optical signal, the signal processor may communicate with the controller to adjust the emission direction to establish communication with the access point or endpoint.

The optical signal emitter may be configured to emit multiple transmitted optical signals in multiple emission directions that are independently adjustable.

With this configuration, the optical wireless communication device may operate in a multiple input multiple output (MIMO) system.

The optical wireless communication device may be part of a mobile endpoint device. In this case, data transfer from the optical wireless communication device (e.g., a dongle or a mobile phone) may be accomplished via a digital communication interface device. The optical wireless communication device may be communicatively connected to the digital communication interface device by wires, or copper or gold interconnects. The digital communication interface device may be a Universal Serial Bus (USB) interface, a Bluetooth interface, or an Ethernet interface. The mobile optical communication device may be communicatively connected to a user device via the digital communication interface device.

The present invention relates to all possible combinations of the features recited in the claims. Other objects, features, and advantages of the inventive concept will become apparent from the following detailed disclosure, from the appended claims, and from the drawings. Features described in connection with one embodiment may also be incorporated in other embodiments, and the advantages of such features are applicable to all embodiments in which the feature is incorporated.

The above and additional objects, features, and advantages of the disclosed devices, methods, and systems are described in the following illustrative, non-limiting example of embodiments of the devices, methods, and systems, with reference to the accompanying drawings. It will be better understood through detailed explanation. As shown in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and are thus provided to illustrate the general structure of embodiments of the present invention. There is. Like reference numbers refer to like elements throughout.
FIG. 1 shows a cross-sectional view of an optical detector. FIG. 2 shows the operation of the optical detector in a cross-sectional view. FIG. 3 shows a cross-sectional view of an alternative configuration of an optical detector. Figures 4(a) and 4(b) show cross-sections of optical detectors according to alternative optical isolators. FIG. 5 shows a cross-sectional view of yet another alternative configuration of an optical detector. 6(a), (b) and (c) show cross-sections of optical detectors with various configurations of the light-receiving surfaces of the lens segments. FIG. 7 schematically depicts an optical wireless communication device including an optical detector for detecting an incoming optical signal. Figures 8(a) and (b) schematically illustrate an optical wireless communication device including an optical detector for determining direction and a controller for controlling a single beam emitter and a multi-beam emitter, respectively. FIG. 9 schematically depicts an optical wireless communication device including an optical detector for detecting an incoming optical signal and a direction sensor for determining direction.

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided for thoroughness and completeness, and will fully convey the scope of this disclosure to those skilled in the art.

Referring first to FIG. 1, a cross-sectional view of an optical detector 100 is shown. Optical detector 100 includes a photodetector 101. The photodetector 101 has a central axis 102 located in a central plane 001 orthogonal to a photodetector plane 002. Optical detector 100 further includes a lens 103 having a first lens segment 131 and a second lens segment 132. Lens segments 131 and 132 are separated by central axis 102. Lens segments 131 and 132 each include a first light receiving surface 133 and a second light receiving surface 134, and similarly include a first light exit surface 135 and a second light exit surface 136, respectively. The light receiving surfaces 133 and 134 are larger than the light exit surfaces 135 and 136. Moreover, the light receiving surfaces 133 and 134 have at least partially a first convex surface and a second convex surface, respectively, for concentrating one or more incoming optical signals.

Light exit surfaces 135 and 136 are in optical contact with photodetector 101.

Lens 103 has a lens field of view 003. First lens segment 131 and second lens segment 132 include segmented fields of view 137 and 138, respectively. Segmented fields 137 and 138 include subsets of lens field 003. Segmented fields of view 137 and 138 have substantially different but overlapping viewing areas 004 about central axis 102 . One way to vary the degree of overlap between fields of view may be by modifying the light receiving surface of the lens segment.

FIG. 2 shows the operation of the optical detector 100 in a cross-sectional view. For certain applications, it may be desirable to achieve enhanced light reception capability for incoming optical signals that are incident from a different direction than the normal direction of the photodetector plane 002. For example, this may be relevant to optical wireless communications where the endpoint device containing the optical detector is most often not directly below the access point. Therefore, to detect an incoming optical signal resulting from an angle of incidence greater than the zero angle of incidence (the angle of incidence 801 is defined by the enclosed angle between the oblique direction 802 of the incoming optical signal and the central axis 102) Increasing the gain, such as increasing the light concentration factor of the lens, is beneficial. For an optical signal originating from a normal direction 803 that is perpendicular to the photodetector plane 002 and parallel to the central axis 102, the optical signal has sufficient strength due to the direct field of view and the shortest distance between the access point and the endpoint. The light collection coefficient may be sacrificed. According to the invention, the light-receiving surfaces 133 and 134 of the lens segments 131 and 132, respectively, can be modified to achieve an increase in the light collection coefficient for angles of incidence greater than 0 degrees, the angles of incidence being Defined by the enclosed angle between the direction of the incoming optical signal and the central axis 102.

In FIG. 2, the first light-receiving surface 133 of the first lens segment 131 has, at least in part, a first convex surface. The first convex surface with non-constant curvature has a first minimum radius of curvature 051 at the first surface point. The first line 055 is perpendicular to the first convex surface at the first surface point of the first minimum radius of curvature 051 and can extend to the central axis 102. A first line 055 encircles the central axis 102 and a first angle 053 that is greater than 0 degrees. Similarly, the second angle 054 subtended by the central axis 102 and the second line 056 is greater than 0 degrees, and the second line 056 is at the second surface point of the second minimum radius of curvature 052. It is perpendicular to the second convex surface and extends to the central axis 102. The first and second minimum radii of curvature 051 and 052 are defined by a virtual circle 005, respectively. In FIG. 2, the first angle 053 and the second angle 054 are the same. Therefore, the first light-receiving surface 133 and the second light-receiving surface 134 are mirror images of each other separated by the central axis 102. Lens segments 131 and 132 are symmetrical and can also be considered rotationally symmetrical.

A diagonal direction 802 of the incoming optical signal is shown coinciding with second line 056. Therefore, the second convex surface of the second light-receiving surface 134 is configured to essentially face an incoming light signal from an oblique direction 802 where the angle of light incidence is greater than 0 degrees. As a result, the light-gathering properties of the lens 103 are at least substantially higher for light originating from oblique positions. This is because the incoming optical signal originating from the normal direction 803 experiences less condensation because the portions of the first light-receiving surface 133 and the second light-receiving surface 134 adjacent to the central plane 001 are substantially concave. It is from. The receiving surfaces 133 and 134 are therefore adapted to provide greater gain for off-axis arriving light (occurring in an oblique direction) than on-axis arriving light (occurring in a normal direction). As a result, the optical detector 100 has the property of being more sensitive to signals originating from larger angles of incidence.

In FIG. 3, a cross-sectional view of optical detector 100 is shown, with lens segments 131 and 132 partially optically isolated from each other by optical isolator 104. In FIG. The optical isolator 104 is an air gap 141 and is arranged symmetrically around the central plane 001. The first light receiving surface 133 and the second light receiving surface 134 have characteristics similar to those shown in FIGS. 1 and 2, respectively. Photodetector 101 includes a first photodetector segment 121 and a second photodetector segment 122 configured around central axis 102 . First lens segment 131 is in optical contact with first photodetector segment 121, and similarly, second lens segment 132 is in optical contact with second photodetector segment 122.

At relatively high angles of incidence, the incoming optical signal may not be completely focused on the associated photodetector segment and therefore may reach the air gap 141. Air gap 141 may be designed to allow at least partial transmission of optical signals on neighboring photodetector segments. Air gap 141 may be designed to reflect a substantial optical signal to the photodetector segment(s) associated with the receiving lens segment. Therefore, by careful examination of the light received by the photodetector and knowing the partial transmittance for different light incidence angles, a robust determination of the direction of emission of the incident optical signal is possible. If the lens segments are completely optically isolated from each other by reflective material, determination of the direction of origin of the incoming optical signal may be possible. If optical detector 100 is desired to be used to detect and demodulate optical signals from an access point, optical isolator 104 or air gap 141 may be designed to have limited optical transmission. . For example, depending on the angle of incidence, light transmission through optical isolator 104 or air gap 141 may be no more than 10% of the light impinging on optical isolator 104 or air gap 141. More preferably, 5% of the light impinging on optical isolator 104 or air gap 141 may be allowed to be transmitted.

4(a) and (b) show cross-sections of an optical detector 100 according to an alternative example of the optical isolator 104. FIG. Note that FIG. 4 includes features, elements and/or functionality shown in FIGS. 1-3 and discussed in the associated text. Therefore, for a better understanding, reference is also made to the figures and the descriptions associated therewith. The same reference numerals in FIGS. 1-4 indicate the same or similar components having the same or similar functions.

In FIG. 4(a), lens segments 131 and 132 are separated by an air gap 141. In FIG. Edge surface 147 facing lens segments 131 and 132 is substantially planar and includes an at least partially transparent material 142, perhaps in the form of a coating. Air gap 141 and at least partially transparent material 142 may together represent optical isolator 104 . By selecting the width of the air gap 141 and the at least partially transparent material 142, tuning of the transmission of light through the optical isolator 104 is possible. The at least partially transparent material 142 may be any or a combination of thin metal or dielectric films (e.g., SiO ₂ , SiN _x , TiO ₂ , and Al ₂ O ₃ ) with reflective properties. .

In FIG. 4(b), the optical isolator 104 is represented by an at least partially transparent material 143 located between adjacent lens segments 131 and 132. The at least partially transparent material 143 may be selected to be fully reflective or partially transparent.

FIG. 5 shows a cross-sectional view of an optical detector 100 similar to FIG. Note that FIG. 5 includes features, elements and/or functionality shown in FIGS. 1-4 and discussed in the associated text. Therefore, for a better understanding, reference is also made to the figures and the descriptions associated therewith. The same reference numerals in FIGS. 1-5 indicate the same or similar components having the same or similar functions.

In FIG. 5, lens 103 has a lens edge surface 149 around the edge of photodetector 101. In FIG. Lens edge surface 149 has a partial coverage. Lens edge surface 149 is shown perpendicular to photodetector plane 002. The partial covering has an outer portion 150 that can be absorbent or reflective and an inner portion 151 that can be reflective. The reflective nature of the inner portion 151 allows folding back of incoming light from high angles of incidence that cannot be focused by the lens 103 onto the photodetector plane 002. Partial coverage may be achieved by a metal sheet or reflective coating configured on the lens edge surface. In an alternative example of optical detector 100, lens edge surface 149 may not have any form of coating. Also, the lens edge surface does not have to be orthogonal to the photodetector plane 002 as shown in FIGS. 1-4.

6(a), (b), and (c) show cross-sections of optical detector 100 with various configurations of light-receiving surfaces 133 and 134 of lens segments 131 and 132, respectively. Note that FIG. 6 includes features, elements and/or functionality shown in FIGS. 1-5 and discussed in the associated text. Therefore, for a better understanding, reference is also made to the figures and the descriptions associated therewith. The same reference numerals in FIGS. 1-6 indicate the same or similar components having the same or similar functions.

In FIG. 6(a), the first light-receiving surface 133 and the second light-receiving surface 134 adjacent to the central plane 001 are shown to be substantially flat. On the other hand, the first light-receiving surface 133 partially has a first convex surface having a first minimum radius of curvature 051 that is a part of the virtual circle 005. In this regard, the second light-receiving surface 134 is shown to have mirror symmetry. A first angle 053 is bounded by central axis 102 and first line 055 and is shown to be approximately 40 degrees. In FIGS. 6(b) and (c), the light receiving surfaces 133 and 134 are shown to include different configurations of convex surfaces, and the first angle 053 and the second angle 054 are the same, approximately 15 degrees to 20 degrees. It has also been shown that the degree of The portions of the first light-receiving surface 133 and the second light-receiving surface 134 adjacent to the central plane 001 are directed toward the photodetector plane 002 so that the tangents can be extended to intersect the central plane 001 and the photodetector plane 002. It is configured to curve. Therefore, the incoming light perpendicular to the normal plane is focused much weaker compared to the configuration shown in FIG. 6(a).

FIG. 7 schematically depicts an optical wireless communication device 200 that includes an optical detector 100 with increased sensitivity for detecting incoming optical signals from larger angles. Note that FIG. 7 includes features, elements and/or functionality shown in FIGS. 1-6 and discussed in the associated text. Therefore, for a better understanding, reference is also made to the figures and the descriptions associated therewith. The same reference numerals in FIGS. 1-7 indicate the same or similar components having the same or similar functions.

Optical wireless communication device 200 further includes a signal processor 201 configured to receive detector signals 007 and 008 from photodetector segments 121 and 122, respectively. Signal processor 201 may be a microprocessor, microcontroller, or one or more comparators. Here, the detector signal can be quantified as the power or amplitude of the detected signal measured by the photodetector segment. For communication purposes, high frequency modulation is used. Therefore, a high pass filter 204 is used to filter the detector signals 007 and 008 before being received by the signal processor 201. The high-pass filter 204 may pass signals of 1 MHz or higher. Demodulation is required to extract data or information from the detector signals 007 and 008. Signal processor 201 may determine which photodetector segments 121, 122 may be used to demodulate and extract data or information from detector signals 007 and 008. Therefore, signal processor 201 may select either or both detector signals 007, 008 for demodulation by demodulation device 206. Potentially, optical wireless communication device 200 including optical detector 100 supports multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) systems. Demodulated signal 207 may be a downlink signal received by optical detector 100. Similar principles apply to photodetectors with only one segment, but in this case signal processor 201 may simply pass the detector signal for demodulation. In this case, for a photodetector with a single segment, the detector signals 007 and 008 are the same, so the signal processor does not need to compare the detector signals.

FIG. 8 schematically depicts an optical wireless communication device 200 including an optical detector 100 for determining the direction of an incoming optical signal. Note that FIG. 8 includes features, elements and/or functionality shown in FIGS. 1-7 and discussed in the associated text. Therefore, for a better understanding, reference is also made to the figures and the descriptions associated therewith. The same reference numerals in FIGS. 1-8 indicate the same or similar components having the same or similar functions.

Optical wireless communication device 200 may also include a low pass filter to filter detector signals 007 and 008 used to determine the direction of the incident light beam. Detector signals 007 and 008 filtered by the low-pass filtered signal are received by a signal processor 201 configured to compare the detector signals 007 and 008. The basis for this comparison can be the fraction of detector signals 007 and 008. An example of a fraction can be the magnitude of the signal detected by a photodetector segment divided by the sum of the detector signal magnitudes from all photodetector segments. By comparing the fractions of detector signals 007 and 008, the direction of the incoming optical signal can be determined. Optical isolator 104, similar to the air gap between lens segments 131 and 132, can promote optical crosstalk. Signal processor 201 may also consider transmission through optical isolator 104 for various angles of incidence for robust direct detection. The maximum fraction of the low frequency response of the detector signal may be used to determine from which photodetector segment the communication signal should be extracted, thus creating a single transimpedance amplifier for communication signal amplification. (TIA) alone may be used.

Alternatively, high-pass filtered optical communication signals from different photodetector segments can be used to determine the direction of the incident beam, but this requires multiple transimpedance amplifiers with high frequency amplification characteristics. shall be.

To determine the relative orientation of the access point(s) or endpoint(s), the bandwidth of the photodetector should be less than 10% of the bandwidth of the incoming optical signal to allow even higher sensitivity. Something can happen. Preferably, the 3 dB frequency bandwidth of the photodetector in the direction sensor can be less than 10% of that of the photodetector in the signal sensor used to detect incoming optical signals at high modulation frequencies. It may be even lower, such as <1% or even <0.1%. If the optical wireless communication signal is modulated to, for example, 100 MHz, direction detection may be performed with the signal low-pass filtered at 1 MHz, or even 100 kHz. Alternatively, a 1 kHz to 100 kHz bandpass filter may be used for direction detection, as near direct current (DC) signals may also need to be filtered out.

In FIG. 8(a), optical wireless communication device 200 also includes an optical signal emitter 202 configured to emit an optical signal 221 in an emission direction that is adjustable within an emitter field of view 225. In FIG. The beam of transmitted optical signal 221 can be narrowed. For example, the optical signal emitter 202 may be configured to emit at a solid angle subtended to less than 60%, preferably less than 30%, and most preferably less than 15% of the lens field of view 003. A controller 203 configured to control optical signal emitter 202 is present in optical wireless communication device 200 . Control of optical signal emitter 202 may include adjustment of emission direction and control of basic emitter characteristics (eg, intensity, modulation frequency, and wavelength adjustment). The controller 203 may also be responsible for receiving downlink or uplink signals 205 from a network or endpoint device connected to the access point, respectively, and converting them to be compatible with optical wireless communication.

The optical detector 100 and optical communication device 200 described above may be suitably used to determine the origin of a plurality of incoming optical signals. As shown in FIG. 8(b), this feature includes an optical signal emitter 202 configured to emit two transmitted optical signals 221 and 222 so that multiple optical communication links can be established. can be utilized for control. Therefore, it is beneficial to be able to control an optical signal emitter 202 with multiple tunable narrow beams to maintain a high-throughput multiple-input multiple-output (MIMO) system with an access point or endpoint. As shown in FIG. 8(b), in the emission direction the two transmitted optical signals 221 and 222 are independently adjustable within the emitter field of view 225.

It should be appreciated that all configurations of optical detector 100 described herein above may be suitable for use in endpoint or access point devices from optical wireless communication systems. The purpose of optical detector 100 may be to detect optical signals and/or determine source or access point location.

Signal processor 201 is communicatively connected to controller 203. Once the direction of the access point is determined by the signal processor 201 from the incoming optical signal, the signal processor 201 may also communicate with the controller 203 to adjust the emission direction to establish communication with the access point or endpoint. good. In FIG. 8, the role of the optical detector 100 is to determine the direction of the incoming optical signal in order to robustly separate the access point(s) or endpoint locations, i.e., it is a direction sensor, and ultimately: The objective is to facilitate the control of optical signal emitters that emit narrow beams.

FIG. 9 schematically depicts an optical wireless communication device 200 that includes an optical detector 100 for detecting an incoming optical signal and a direction sensor 900 for determining the direction of the incoming optical signal. Note that FIG. 9 includes features, elements and/or functionality shown in FIGS. 1-8 and discussed in the associated text. Therefore, for a better understanding, reference is also made to the figures and the descriptions associated therewith. The same reference numerals in FIGS. 1-9 indicate the same or similar components having the same or similar functions.

In FIG. 9, direction sensor 900 includes an optical element 901 and a segmented detector 902 used to determine the direction of an incoming optical signal. Optical element 901 can be an imaging or non-imaging optic. For direction detectors, various known configurations in the art may be considered. Sensor signals 903 and 904 pass through low pass filter 220 and are received by signal processor 201. Signal processor 201 is configured to determine direction based on a comparison of sensor signals 903 and 904. Similar to FIG. 7, optical detector 100 is used to detect optical signals from large angles of incidence with increased sensitivity that are ultimately used to extract data or information.

It is noted that the embodiments described above are illustrative rather than limiting, and that those skilled in the art can design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage. The various aspects described above may be combined to provide additional benefits. Furthermore, those skilled in the art will understand that two or more embodiments may be combined.

Claims (10)

An optical detector for receiving incoming optical signals from multiple directions, the optical detector comprising:
a photodetector having a central axis located in a central plane perpendicular to the photodetector plane;
a lens having a first lens segment and a second lens segment separated by the central plane;
including;
The photodetector includes a first photodetector segment and a second photodetector segment configured around the central axis,
the first lens segment includes a first light receiving surface and a first light exit surface, the first light exit surface facing the photodetector;
the second lens segment includes a second light receiving surface and a second light exit surface, the second light exit surface facing the photodetector;
The first light-receiving surface includes a first convex surface having a non-constant curvature, the first convex surface having a first minimum radius of curvature at a first surface point,
the second light-receiving surface includes a second convex surface having a non-constant curvature, the second convex surface having a second minimum radius of curvature at a second surface point;
The first lens segment and the second lens segment are at least partially optically isolated from each other by an air gap between the first and second lens segments; two lens segments are positioned about the central axis and have mutually opposing substantially planar edge surfaces, the edge surfaces comprising an at least partially transparent material;
a first angle subtended by the central axis and a first line is greater than 0 degrees; the first line is perpendicular to the first convex surface at the first surface point; It extends to
a second angle subtended by the central axis and a second line is greater than 0 degrees, the second line is perpendicular to the second convex surface at the second surface point, and the second angle is greater than 0 degrees; Optical detector that extends up to The optical detector according to claim 1, wherein the first angle and the second angle have the same value in a range of 5 degrees to 45 degrees. The optical detector according to claim 1 or 2, wherein the first light-receiving surface and the second light-receiving surface have a portion adjacent to the central plane that is substantially flat or concave. The optical detector of claim 1 or 2, wherein the first light receiving surface and the second light receiving surface have portions adjacent to the central plane that curve toward the photodetector plane. 5. The method of claim 1, wherein the first light exit surface is in optical contact with the first photodetector segment and the second light exit surface is in optical contact with the second photodetector segment. Optical detector according to any one of the items. Optical detector according to any one of claims 1 to 5, wherein the air gap has a width in the range of 10 to 100 micrometers. Optical detector according to any one of claims 1 to 6, wherein the lens has a certain number of lens segments, and the photodetector has a number of photodetector segments that is the same as or an integral multiple of the number of lens segments. . The optical detector according to claim 1;
a signal processor configured to receive a plurality of detector signals respectively generated by the first photodetector segment and the second photodetector segment;
a demodulation device;
An optical wireless communication device comprising:
the signal processor is configured to select at least one of the plurality of detector signals;
An optical wireless communication device, wherein the demodulation device is configured to demodulate at least one of the plurality of detector signals to extract data. The optical wireless communication device further includes:
an optical signal emitter configured to emit a transmitted optical signal in an emission direction that is adjustable;
a controller configured to control the optical signal emitter;
including;
the signal processor is configured to determine the direction of an incoming optical signal by comparing the plurality of detector signals;
9. The optical wireless communication device of claim 8, wherein the signal processor is communicatively connected to the controller to adjust the emission direction of the optical signal emitter based on the direction of the incoming optical signal. The optical wireless communication device further includes:
an optical signal emitter configured to emit a transmitted optical signal in an emission direction that is adjustable;
a controller configured to control the optical signal emitter;
a direction sensor including an optical element and a segmented detector;
including;
the signal processor is configured to determine the direction of an incoming optical signal by comparing a plurality of sensor signals generated by a segmented photodetector;
9. The optical wireless communication device of claim 8, wherein the signal processor is communicatively connected to the controller to adjust the emission direction of the optical signal emitter based on the direction of the incoming optical signal.

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